1. Field of Invention
The present invention relates to novel proteins from Piscirickettsia salmonis. The present invention also pertains to the nucleic acids that encode these proteins. The present invention further relates to a process of preparing a vaccine against salmonid rickettsial septicemia (SRS) using the proteins as antigens, or the nucleic acids in bacterial hosts to express such antigens. The present invention also relates to bacterins and viral antigens that can be combined to form a vaccine against SRS. The present invention also pertains to vaccines for preventing SRS, as well as preventing other bacterial and/or viral infections in fish.
2. Background
Salmonid rickettsial septicemia (SRS), also known as piscirickettsiosis, is a fatal disease in salmonids. Although the etiological agent for SRS was identified in the late 1980's as Piscirickettsia salmonis, antibiotics proved to be an unsuccessful treatment, due, at least in part, to the intracellular nature of this bacterium [Bravo and Campos, FHS/AFS Newsl. 17:3 (1989); U.K. Patent Application 2 356 632]. As a consequence of the lack of a viable treatment, millions of farmed salmon die of SRS each year just in southern Chile alone [Smith et al., Dis. Aquat. Organ. 37(3):165-172 (1999)]. In addition, recent reports demonstrate a link between Piscirickettsia-like bacteria and disease syndromes in non-salmonid fish [see, Mauel and Miller, Veterin. Microbiol. 87(4):279-289 (2002)].
The Salmonidae family (salmonids) includes salmon, trout, char, and whitefish. Salmonids serve both as a food source and as a game fish. Moreover, in countries such as Chile, Norway, Canada, the United Kingdom, Ireland, and the United States, salmonids have become an important commercial product due, at least in part, to the ability of fish farmers to artificially spawn, incubate and raise the salmonids in captivity.
Unlike fish originating in the wild, those raised in captivity are amenable to prophylactic treatments such as vaccination. So far, several potential vaccines have been described, such as one based on a specific Piscirickettsia salmonis antigen, a 17 kDa lipoprotein OspA [U.K. Patent Application 2 356 632; see also WO 01/68865 A2]. Additional potential vaccines against Piscirickettsia salmonis are described by WO05035558 A2 and WO2006037383 A1, the contents of which are hereby incorporated by reference in their entireties. These published international patent applications describe an isolated Piscirickettsia salmonis Psp45 protein and antigenic fragments thereof, as well as other SRS antigens.
The coding sequence for Psp45 protein is contained by a recombinant Chilean strain of Yersinia ruckeri that has been deposited (BCCM accession No. LMG P-22044). The nucleotide coding sequence of the Psp45 protein within the deposited recombinant Yersinia ruckeri is included within SEQ ID NO: 16. The amino acid sequence of the Psp45 protein within the deposited recombinant Yersinia ruckeri is SEQ ID NO: 7 [the amino acid sequence of SEQ ID NO: 8 is identical to that of SEQ ID NO: 7, except SEQ ID NO: 8 lacks the sequence for the signal peptide.]
In addition to Piscirickettsia salmonis, other pathogens are known to cause disease in farmed fish, including salmon. One such pathogen is the Infectious Pancreatic Necrosis virus (IPN virus), which is an unenveloped, icosahedral, bisegmented dsRNA virus. The IPN virus contains one main structural protein, VP2 (52 kDa) and three additional proteins, VP1 (90 kDa), VP3 (30 kDa) and VP4 (28 kDa). VP2 is the main protein of the outer capsid and is therefore immunologically important in recognition and bonding of the virus. VP1 is thought to be a polymerase, whereas VP3 and VP4 are internal proteins. VP4 is believed to correspond to a form of VP3 fragment formed during viral differentiation [see, WO 02/38770 A1, the contents of which are hereby incorporated by reference in their entireties]. Nucleotide and amino acid sequences for VP2 and VP3 have been determined [see, Havarstein et al., J. Gen. Virol. 71:299-308 (1990); Pryde et al., Archives of Vir. 129:287-293 (1992)].
There, therefore remains a need to provide new safe and effective vaccines against Piscirickettsia salmonis. In addition, there remains a need to identify new antigens from Piscirickettsia salmonis that can be used in such vaccines. Furthermore, there is a need to obtain nucleic acids that encode such antigens. In addition, there is a need to provide methods of vaccinating fish to protect them from Piscirickettsia salmonis and Piscirickettsia-like bacteria. Furthermore, there is a need to provide vaccines that can protect fish against Piscirickettsia salmonis and other unrelated pathogens, particularly those of commercial importance, such as the IPN virus.
The citation of any reference herein should not be construed as an admission that such reference is available as “prior art” to the instant application.